The present invention relates to films used principally in packaging food products, and more specifically, to improved strands of tubular casings for packaging sausage and other meat products, and methods for their manufacture.
Food casings fabricated from either edible or nonedible films have been widely used for many years in processing and packaging various meat products like frankfurters, sausages, bolognas, hams, deli loaves and the like. Nonedible cellulose type casings, for example, are prepared by extruding tubular viscose into a coagulating bath where it is regenerated, washed, plasticized, dried and formed into flat tubular films by winding onto large reels. Edible type casings, especially those prepared with collagen are manufactured as hollow, thin-walled tubes also of substantial length.
For convenience in handling and stuffing, it has been standard practice of casing manufacturers to convert much of such film into pleated, hollow tubular strands or sticks on high speed shirring machines where, for example, up to 200 feet of casing material is pleated into sticks generally ranging from about 5 to 30 inches in length. Such strands are packaged and shipped to meat processors and packers where they are automatically fed onto horns and stuffed with meat emulsion, etc., to their fully extended lengths.
During earlier years when casings were stuffed manually, operators would simply deshirr a short length of casing at the stuffing site to form an end-closure so as to prevent loss of meat from the receiving end of the strand. However, in the case of modern high speed automated filling equipment such operations have dictated that end-closures be formed during manufacture of casings, rather than during filling.
Various methods have been proposed for making end-closures on shirred strands. Closures may be formed which extend outwardly from the strand, or alternatively, they can be recessed inside strand bores. For instance, U.S. Pat. No. 3,965,537 discloses a method for sealing ends of edible collagen casings by joining opposing internal surfaces and heat sealing at an oblique angle across the full width of the deshirred end. Although this method reduces the film needed in forming end-closures it does not provide for venting air when the stuffing horn indexes the casing. This results in premature deshirring of the strand, which in turn causes frequent casing blow-outs and lost production from downtime. In addition, the oblique heat seal is not always reliable in providing the strength and resiliency needed to absorb the initial shock of meat emulsion being forced into the casing under high pressure. This can result in a relatively high rate of casing failure.
U.S. Pat. No. 4,536,175 discloses an alternative method for making end-closures for collagen casings. Instead of heat sealing, the end-closure is formed inside the bore of the strand. Film from the strand end is wound into a plug which is positioned centrally inside the bore without fully deshirring the film as the plug is being wound. Similarly, U.S. Pat. No. 3,162,893 provides for a twisted end-closure without heat sealing, except that the closure remains on the outside of the strand. The casing end-closure is twisted upon itself or tied closed. Although the latter methods reduce the incidence of casing blow-out during stuffing each of the immediate foregoing methods require significant lengths of film, up to 14 inches, in forming their respective twisted end-closures. This results in a rather significant amount of waste because the film used in forming the closure is unavailable for packaging during stuffing operations, thereby leading to higher production costs. Accordingly, there is a need for more economic and reliable end-closures for shirred strands, and more particularly, to improved end-closures for shirred collagen casings and methods of manufacture.